1. Field of the Invention
This invention relates to a pneumatic tire, and more particularly to an improvement of a bead portion in a pneumatic tire provided with a bead core having a polygonal form at its cross section.
2. Description of Related Art
In a bead portion of a heavy duty pneumatic tire, a portion of a carcass is wound around a bead core having, for example, a hexagonal form at its cross section from an inside of the tire toward an outside thereof in a radial direction and a bead filler is arranged above an outer periphery of the bead core between a main portion of the carcass and a turnup portion thereof. For the purpose of enhancing the rigidity of the bead portion and hence rigidities in all directions of the tire, it is widely and generally practiced to arrange at least one chafer made of nylon cords, steel wires or the like along the bead filler.
In the conventional chafer, a plurality of nylon cords, steel wires or the like are extended at a state of slightly inclining with respect to a phantom radial line segment viewed from a side face of the tire. Therefore, there is a problem that each nylon cord or the like, particularly an outer end thereof in the radial direction is easily peeled off from rubber during the repetitive rotation of the tire under loading, particularly due to the deflection deformation of the bead portion and side-wall portion.
And also, such a chafer is apt to easily cause the deformation, peeling or the like of the cord in the outer portion in the radial direction, which increases a size increasing quantity, accompanied with the increase of winding radius during the formation of a green tire, particularly at a shaping step thereof. As a result, the chafer is arranged only in the vicinity of the bead core. Furthermore, an extending angle of the nylon cord or the like and an arranging width of the chafer in the radial direction and the like are changed by the increase of the winding radius at the shaping step, and also an arranging density of the nylon cord or the like after the completion at the shaping step gradually decreases toward the outside of the chafer in the radial direction, so that it is difficult to give the rigidity to the bead portion as is expected.
It is, therefore, an object of the invention to solve the aforementioned problems of the conventional technique and to provide a pneumatic tire capable of sufficiently realizing a desirably adequate rigidity in a bead portion by eliminating a peeling fear of cord or the like and arranging cords or the like in required position and form as is expected in this type of reinforcing layer arranged along the bead filler.
According to the invention, there is the provision of in a pneumatic tire comprising a bead portion, a carcass wound around a bead core having a polygonal form at its cross section from an inside of a tire toward an outside thereof in a radial direction and a bead filler arranged on an outer periphery of the bead core between a main portion and a turnup portion of the carcass, an improvement wherein a reinforcing layer comprised of an organic fiber cord(s) or a metal wire(s) extended substantially in a circumferential direction of the tire is arranged in a position adjacent to the bead filler.
In the invention, the reinforcing layer is possible to have a structure that a plurality of circular rings each made of the organic fiber cord or the metal wire are arranged concentrically, but is preferable to have a spirally wound structure of one or more organic fiber cords or metal wires.
In the tire according to the invention, the organic fiber cord or the like constituting the reinforcing layer, for example monofilament cord or multi-filament cord is extended substantially in the circumferential direction of the tire, whereby the revelation of cord ends as described in the conventional technique can be prevented and also the peeling of these cord ends can effectively be prevented. This is particularly remarkable when the reinforcing layer has a concentrically arranging structure of plural rings or a spirally wound structure.
And also, the reinforcing layer comprised of the cord or the like extending substantially in the circumferential direction of the tire effectively contributes to increase the rigidity of the bead portion in various directions of the tire such as up and down directions and lateral direction and front and back directions. Particularly, the reinforcing layer can largely increase the rigidities in the lateral and front and rear directions of the tire among the above rigidities to ensure the realization of excellent steering stability and the like.
When the reinforcing layer has the spirally wound structure of one or more organic fiber cords or metal wires, it can simply be formed by spirally and continuously winding the cord or the like, and also such a wound form can easily be maintained. Therefore, the reinforcing layer can be simply, easily and accurately arranged in a given position of a green tire and hence a product tire without damaging the wound form of the cord or the like by sticking the reinforcing layer to a required position of the bead filler stood up on the bead core through adhesion or the like prior to the folding the turnup portion of the carcass, the sidewall portion and the like in the building of the tire, e.g. at the shaping step, or by setting the bead filler provided with the bead core and stuck on the required portion with the reinforcing layer at a given position in a stand-up posture. Thus, the rigidity of the bead portion can be increased as required, and also it is easy to incorporate such a bead portion rigidity in the design of the tire.
The reinforcing layer may be arranged in at least one of inner and outer faces of the bead filler. In this case, the reinforcing layer may be arranged over substantially a whole or a part of the bead filler in the radial direction or at given intervals in the radial direction of the bead filler.